Bài 1B:

a) 

\(\dfrac{-1}{16}+\dfrac{-1}{24}\\ =\dfrac{-3}{48}+\dfrac{-2}{48}\\ =\dfrac{-5}{48}\)

b) 

\(\dfrac{-1}{8}-\dfrac{3}{20}\\ =\dfrac{-5}{40}-\dfrac{6}{40}\\ =\dfrac{-11}{40}\)

c) 

\(-\dfrac{18}{10}+0,4\\ =\dfrac{-9}{5}+\dfrac{2}{5}\\ =\dfrac{-7}{5}\)

d) 

\(6,5-\left(-\dfrac{1}{5}\right)\\ =\dfrac{13}{2}+\dfrac{1}{5}\\ =\dfrac{65}{10}+\dfrac{2}{10}\\ =\dfrac{67}{10}\)

Lời giải:

PT $\Leftrightarrow (x-1)\left(\frac{1}{13}+\frac{1}{14}-\frac{1}{15}-\frac{1}{16}\right)=0$

Hiển nhiên $\frac{1}{13}+\frac{1}{14}>\frac{1}{15}+\frac{1}{16}$

$\Rightarrow \frac{1}{13}+\frac{1}{14}-\frac{1}{15}-\frac{1}{16}>0$

$\Rightarrow x-1=0$

$\Rightarrow x=1$

Vậy PT có nghiệm duy nhất $x=1$.

P/s: Bạn lưu ý lần sau gõ đề bằng công thức toán (biểu tượng $\sum$ góc trái khung soạn thảo) để mọi người đọc hiểu đề của bạn hơn nhé. 

a,

\(-\frac{9}{11}<\frac 9x<-\frac{9}{13}\\\Rightarrow \frac{-11}{9}>\frac x9 >\frac{-13}{9}\\ \Rightarrow -11>x>-13\)

b, 

\(-\frac35<\frac 9x <-\frac49\\\Rightarrow -\frac53>\frac x9>-\frac 94\\\Rightarrow \frac{-60}{36}>\frac{4x}{36}>\frac{-81}{36}\\\Rightarrow -60>4x>-81\\\Rightarrow -15>x>-\frac{81}{4}\)

a: \(1,25:\left(\dfrac{1}{2}-1\dfrac{1}{2}\right)-1,75\cdot\left(-20\%\right)\)

\(=\dfrac{5}{4}:\left(-1\right)-\dfrac{7}{4}\cdot\dfrac{-1}{5}\)

\(=-\dfrac{5}{4}+\dfrac{7}{20}=\dfrac{-25}{20}+\dfrac{7}{20}=-\dfrac{18}{20}=-\dfrac{9}{10}\)

b: \(\left(2,2+40\%\right):\left(\dfrac{1}{2}-1,25:20\%\right)\)

\(=\left(2,2+0,4\right):\left(0,5-1,25:0,2\right)\)

\(=2,6:\left(-5,75\right)=-\dfrac{52}{115}\)

c: \(\left[\dfrac{3}{4}-1,25:\left(-1\dfrac{1}{2}\right)\right]:\left(3,75-\dfrac{1}{2}:0,25\right)\)

\(=\left(\dfrac{3}{4}-\dfrac{5}{4}:\dfrac{-3}{2}\right):\left(\dfrac{15}{4}-\dfrac{1}{2}:\dfrac{1}{4}\right)\)

\(=\left(\dfrac{3}{4}+\dfrac{5}{4}\cdot\dfrac{2}{3}\right):\left(\dfrac{15}{4}-2\right)\)

\(=\left(\dfrac{3}{4}+\dfrac{5}{6}\right):\dfrac{7}{4}=\left(\dfrac{9}{12}+\dfrac{10}{12}\right):\dfrac{7}{4}\)

\(=\dfrac{19}{12}\cdot\dfrac{4}{7}=\dfrac{19}{21}\)

d: \(0,75\cdot\dfrac{-17}{13}-\dfrac{3}{4}\cdot\dfrac{-4}{13}-1,25\)

\(=0,75\cdot\dfrac{-17}{13}+\dfrac{3}{4}\cdot\dfrac{4}{13}-1,25\)

\(=0,75\cdot\left(-\dfrac{17}{13}+\dfrac{4}{13}\right)-1,25\)

=-0,75-1,25

=-2

Chọn C

Câu C nha bạn.

Tick mình được hong?

a: \(2xy+x-y+xy^2+2xy\)

\(=x-y+xy^2+\left(2xy+2xy\right)\)

\(=x-y+xy^2+4xy\)

b: \(5xy^2+4y-4x\cdot2y^2\)

\(=4y+5xy^2-8xy^2\)

\(=4x-3xy^2\)

c: \(\sqrt{25}+\sqrt{36}+\sqrt{49}+...+\sqrt{100}\)

=5+6+7+8+9+10

=15+15+15

=45

d: Đặt \(A=1+4+9+16+...+9801+10000\)

Đặt \(B=1+8+27+...+729+1000\)

 \(A=1+4+9+...+10000\)

\(=1^2+2^2+...+100^2\)

\(=\dfrac{100\left(100+1\right)\left(2\cdot100+1\right)}{6}\)

\(=\dfrac{100\cdot101\cdot201}{6}\)

\(B=1+8+27+...+1000\)

\(=1^3+2^3+...+10^3=\left(1+2+...+10\right)^2\)

\(=55^2\)

=>\(A-B=\dfrac{100\cdot101\cdot201}{6}-55^2=335325\)

b: \(\dfrac{1}{2^2}< \dfrac{1}{1\cdot2}=1-\dfrac{1}{2}\)

\(\dfrac{1}{3^2}< \dfrac{1}{2\cdot3}=\dfrac{1}{2}-\dfrac{1}{3}\)

...

\(\dfrac{1}{100^2}< \dfrac{1}{99}-\dfrac{1}{100}\)

Do đó: \(A=\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{100^2}< 1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{99}-\dfrac{1}{100}\)

=>\(A< 1-\dfrac{1}{100}\)

=>A<1

=>0<A<1

=>A không là số tự nhiên

a: \(A=1+4+9+...+10000\)

\(=1^2+2^2+...+100^2\)

\(=\dfrac{100\left(100+1\right)\left(2\cdot100+1\right)}{6}\)

\(=\dfrac{100\cdot101\cdot201}{6}\)

\(B=1+8+27+...+1000\)

\(=1^3+2^3+...+10^3=\left(1+2+...+10\right)^2\)

\(=55^2\)

=>\(A-B=\dfrac{100\cdot101\cdot201}{6}-55^2=335325\)